Cryogenic cooling apparatus for cooling radiation detectors to cryogenic temperatures are well known and widely used in x-ray spectrometry and electron microscopy. In such spectrometers x-rays are detected from a specimen being spectrometrically examined, and radiation from the specimen is detected by a cryogenically cooled detector to convert the radiation to electrical signals in a known way for spectroscopic analysis.
Such detectors involve elongated structures known in the art as cold fingers. Such a cold finger is cantilevered from a Dewar arrangement so as to place a detector within the region of an electron beam of a microscope, for example, adjacent to the specimen. The interior of the electron microscope and the region surrounding the cold finger are within an evacuated chamber, and cooling of the detector is accomplished by the cold finger being thermally conductively connected to a source of cryogenic cooling, such as the Dewar containing liquid nitrogen.
Such structures may be seen by way of previous patents U.S. Pat. Nos. 5,235,817 and 5,274,237 of which the present inventor is a common inventor and which patents are assigned to the same assignee as the present application. In these previous prior art cryogenically cooled arrangements, the radiation detector is supported at the end of a cantilevered cold finger and maintained in the vicinity of the specimen. Because of thermal contraction occurring when the detecting unit is cooled, the radiation detector is subjected to movement on the cold finger support. Such movement caused by temperature changes at temperatures, such as 77.degree. K., the temperature of liquid nitrogen, for example, results in movement of the detector crystal of about 0.040 to 0.060 inches. Such movement of the detector crystal significantly decreases the performance and sensitivity of the detector crystal.
Current practice according to the prior art fixes the cold finger at an interface between a detector cap and a specimen housing. This allows between 0.040 and 0.060 inches of detector crystal movement as the cold finger shrinks.